Fan drives are utilized for cooling the internal combustion engine of a motor vehicle and are, as a rule, mounted in the engine compartment of the motor vehicle behind a heat-transfer unit or an assembly unit of several heat-transfer units, for example, a coolant radiator, a charge-air cooler and/or a coolant condenser.
It is known to not drive the fan directly by the engine but, instead, by a controlled clutch, for example, a fluid friction clutch. Because of the control, an efficient and energy-saving cooling is achieved wherein the fan is only switched on when cooling is needed and, if needed, at different rpms adapted to the cooling requirement. The fluid friction clutch operates in accordance with the principle of shear friction. Here, a viscous medium, especially silicone oil, is used for the torque transmission. The torque transmission takes place with slippage wherein the output rpm is less than the drive rpm. For this reason, heat arises because of the friction and this heat must be conducted away to maintain a permissible operating temperature of the clutch. Accordingly, the clutch has cooling ribs on the outer side of its housing over which ambient air passes. This cooling effect is not adequate at higher capacities, especially, at higher drive rpms. The danger here is presented that the silicone oil will overheat and this can then lead to the silicone oil losing its transfer capability which can lead to a blockage of the clutch.
For this reason, a second fan wheel is suggested in German patent publication 10 2007 037 733. This second fan wheel is mounted ahead of the fluid friction clutch in the air flow direction and so effects an additional targeted cooling of the forward housing part.
It is further known to control the rpm of a fluid friction clutch electromagnetically as disclosed, for example, in U.S. Pat. No. 5,937,983. For this purpose, an electromagnetic coil is stationarily mounted in the air flow direction ahead of or rearward of the fluid friction clutch. The electromagnetic coil actuates a valve mechanism disposed in the interior of the clutch. As disclosed in U.S. Pat. No. 5,555,963, the electromagnetic coil can also be mounted in the interior of the fluid friction clutch, especially, in the supply chamber.
The fluid friction clutch is often journalled via its housing on a drive shaft which can also be the crankshaft of the internal combustion engine. The fluid friction clutch is in this way preferably journalled via a roller bearing. This roller bearing is disposed at the rear side of the clutch, that is, the side facing toward the internal combustion engine. Since the fluid friction clutch also carries the weight of the fan, this roller bearing is subjected to intense loads and is furthermore not adequately cooled because the main cooling-air flow passes over the forward side of the clutch housing.